WO2007010848A1

WO2007010848A1 - Resin-coated sand for use in cast steel, casting mold made of the sand, steel casting casted using the casting mold

Info

Publication number: WO2007010848A1
Application number: PCT/JP2006/314046
Authority: WO
Inventors: Toshio Tanaka; Ken Ogasawara; Eiji Nohara
Original assignee: Komatsu Ltd.; Asahi Organic Chemicals Industry Co., Ltd.; Komatsu Castex Ltd.
Priority date: 2005-07-15
Filing date: 2006-07-14
Publication date: 2007-01-25
Also published as: JP4545192B2; CN101222992A; CN101222992B; JPWO2007010848A1

Abstract

A resin-coated san for use in cast steel, comprising a casting sand, a phenolic resin in an amount of 2.5 to 5.0% by weight relative to the amount of the casting sand, potassium nitrate and vinsole. A steel casting manufactured by the casting on a casting mold which is molded using the resin-coated sand can effectively prevent the occurrence of hot-cracking or bath wrinkle even in a thin and large-sized article.

Description

Specification

Resin coated sand for steel, steel mold made of the same sand and steel products made by the same mold

Technical field

[0001] The present invention relates to a resin-coated sand suitable for steel, a steel-coated steel mold made of the resin-coated sand, and a steel product forged from the steel mold. In particular, the present invention relates to a resin-coated sand that can effectively reduce the occurrence of hot cracks and hot water wrinkles that tend to occur in steel products, a steel mold made of the same sand, and a steel product made from the same mold.

Background art

[0002] In recent years, steel articles with high strength have been attracting attention in order to ensure a desired strength and to achieve light weight in automobiles and construction machines. In particular, in order to reduce the weight of steel objects, it is expected to establish a hollow thinning technology. In the field of pig steel, this hollow thinning technique, for example, the shell mold method described below has been known for a long time and has been used in various technical fields.

[0003] By the way, when manufacturing steel products, it is known that the amount of solidification shrinkage of the molten metal at the time of forging is nearly twice as large as that of iron products and aluminum alloy products. For example, when manufacturing a pig steel having a hollow structure, solidification shrinkage of the molten metal occurs, so that the shrinkage is constrained by a core (saddle type) that forms a hollow portion. For this reason, there was a problem that hot cracks occurred in the porcelain. Thus, the hot cracks that occurred in the steel were required to be repaired by removing them after forging and refinishing them into the desired product shape. For example, as a repairing work, a hot crack generated in the steel is first removed by a grinder or gouging process. Next, build-up welding is performed on the part, and further grinder processing is performed. As a result, it is possible to manufacture a steel plate having a desired shape from which hot cracks have been removed.

[0004] However, if such hot crack repair work in steel is increased, the productivity of steel is reduced and the cost is increased, resulting in a problem of poor economic efficiency. I got it. Furthermore, when manufacturing steel frames with complex shapes, On the other hand, it may be very difficult to perform repair work. In such a case, it was necessary to start the forging work of steel products from the beginning.

[0005] In order to deal with such problems, for example, carbon dioxide (CO

(2 gas), a method called the CO gas method using the hardening of water glass (sodium oxalate) is adopted.

2

It is used. In this carbon dioxide gas system, water glass, which is an inorganic binder, is blended in an amount of about 5% by weight based on the sand. After forming this kneaded product, carbon dioxide gas is passed through to gel the water glass and cure the mold.

[0006] When steel is manufactured using a steel mold made by this carbon dioxide gas method, when the molten steel is poured into the steel cavity and solidifies and shrinks, the inorganic binder is removed by the heat of the melt. Can be softened. As a result, the sand used in the mold can move in the direction of filling the gap, and the mold itself contracts, reducing the binding force of the core against solidification shrinkage of the steel. It becomes possible. However, in the mold (core) formed by such a carbon dioxide gas system, the glazed sand becomes a moisture state containing moisture at the time of molding. For this reason, it becomes difficult to uniformly fill the core model with the core sand during core molding. In addition, in this case, there was a tendency that the density of the saddle type became higher than necessary.

[0007] Therefore, even when forging is performed using a mold obtained by the carbon dioxide method, the mold does not sufficiently contract when the molten metal solidifies and shrinkage, and the effect of preventing hot cracking may not be expected. . In addition, since water glass is used as a binder, the sand that forms the core during forging may sinter due to the heat of the molten metal and the core sand may be strongly baked. It was. If the core sand is baked in this way, it becomes extremely difficult to disintegrate and remove the core after producing the steel. For this reason, there has been a problem that productivity is lowered.

[0008] On the other hand, a dry seal mold method is known as another mold forming method for steel. In this shell mold method, coconut resin is coated as an organic binder on dredged sand, and the resulting resin-coated sand (RCS) is filled into a preheated model. The resin coated with the sand is condensed by the heat of the model to form a shell layer. The shell layer is further heated and cured together with the model, and then the shell layer is released from the model cover to produce a saddle shape.

[0009] When the mold produced by such a shell mold method is used as the core of a steel forging, Phenolic sebum, which is a binder, is decomposed in a high temperature forging process. For this reason, when taking out the core from the hollow portion of the steel frame after forging, the core can be easily collapsed. Therefore, there is an advantage that the core can be easily taken out.

[0010] An invention relating to a phenol resin composition used as a saddle type material in such a shell mold method is disclosed in JP-A-57-68240 (Patent Document 1). The phenolic resin composition described in Patent Document 1 is a low-molecular composition composed of three components: phenol, bisphenol A, and a separated component or derivative in the residue generated when bisphenol A is produced. It is a phenolic resin composition exhibiting expansibility.

[0011] By using such a low-expansion phenolic resin composition to make a mold by a shell mold method, the mold is rich in flexibility and has better flexibility. have. Further, it is said that by performing forging using a mold having such characteristics, it is possible to suppress the occurrence of hot cracks and pinholes (gas defects) in the object. Here, the term “sexuality” refers to the property that the mold shrinks together with the bowl, and the performance of the bowl that can withstand the shrinkage and expansion of the molten metal.

[0012] In recent years, in the manufacture of steel products, it has been required to reduce the thickness of the steel products as much as possible in order to reduce the weight of the steel products. However, when forging steel products, there has been a problem that hot cracks are likely to occur if the thickness of the products is reduced due to light weight. Therefore, for example, when manufacturing a thin steel product, even if a mold made of a low expansion phenolic resin composition as described in Patent Document 1 is used, the composition of the resin It was difficult to sufficiently prevent the occurrence of hot cracks in thin-walled steel by only the effect of preventing the hot cracks depending on the flexibility of the saddle type based on the material and the nature. Therefore, particularly in the production of thin-walled steel products, it has been desired to develop a technology that can more effectively prevent the occurrence of hot cracks.

[0013] Furthermore, when manufacturing thin-walled steel products, the heat of the injected molten metal is easily taken away by the bowl (core), and the flow of the molten metal may not be made uniform in the bowl-shaped cavity. As described above, when the molten metal flow becomes poor and the hot water flowability (molten metal flowability) decreases, there is a problem that uneven hot water is generated on the surface of the forged steel product. “Yojiwa” means JIS G 0588 V, “Wrinkles with visible bottom caused by too low pour temperature, too low pour speed” It is defined and grades 1-5 are classified for the state of hot water wrinkles. As described above, for example, the RCS described in Patent Document 1 cannot be expected to completely solve the problem of hot water wrinkles occurring in the steel, and development of further technology for effectively reducing the hot water wrinkles. Has been strongly demanded.

[0014] By the way, compared with the above-described steel structure forging, the strength of the molten metal is quite different from that of the non-ferrous metal structure (for example, aluminum), and for the shell mold method. Inventions relating to materials are disclosed in Japanese Patent Publication No. 31-7256 (Patent Document 2) and Japanese Patent Application Laid-Open No. 9-57391 (Patent Document 3). When producing such a non-ferrous aluminum, it is generally known that the forging temperature is lower than that of steel. Specifically, when manufacturing steel products, the forging temperature is about 1500-1600 ° C, whereas for aluminum, the forging temperature is about 660-700 ° C, which is extremely low! ,.

[0015] In the forging of aluminum, the following problems have occurred due to the low forging temperature. In other words, when a mold made by the shell mold method is used as a core, decomposition of the mold-type binder (phenolic resin) does not occur at the production temperature of the film. For this reason, when producing a hollow aluminum casing, the core remains in the hollow interior of the casing in a state of maintaining high strength after forging. Therefore, a great deal of labor and energy was required to take the core out of the box and destroy it.

[0016] In order to solve such problems, Patent Document 2 adds 0.5 to 20% by weight of a substance that imparts or transmits oxygen (for example, lead tetraphosphate or potassium nitrate). The use of phenol resin as a binder in RCS is described. By using a substance that imparts or transmits oxygen in this way, it is said that the decomposition of the binder can be promoted to improve the saddle-type disintegration property. For example, the core binder can be thermally decomposed by forging a hollow aluminum bowl and then subjecting the obtained mold with a core to heat treatment (sand baking). As a result, the strength of the core is reduced, and the core can be easily taken out from the hollow casing.

[0017] Further, in Patent Document 3, the RCS described in Patent Document 2 does not supply a sufficient amount of heat to the saddle, and the disintegration of the saddle is insufficient at a low temperature region. Point out that. On top of that, Patent Document 3 shows sufficient saddle-shaped disintegration even in such a low temperature region. As RCS, refractory particles, phenolic resin, oxygen-containing hydrocarbon compounds (lower carboxylic acids, etc.) with an oxygen content of 25% by weight or more, and alkali metal nitrates (nitric acid lithium, sodium nitrate, etc.) We have proposed RCS, which has a saddle-type disintegration improver contained at a predetermined ratio as an essential component. By including such a disintegration improver in the RCS, it is said that, for example, the saddle-shaped disintegration property in a low temperature range of 300 to 350 ° C. can be improved.

[0018] However, Patent Documents 2 and 3 are intended only to improve saddle-type disintegration in a non-ferrous metal having a low forging temperature such as aluminum described above. For this reason, there is no discussion at all regarding the problems related to hot cracks and hot water wrinkles that occur in the wrought goods, and specific means for suppressing the occurrence of hot cracks and hot water wrinkles are described. Absent.

In these Patent Documents 2 and 3, potassium nitrate is exemplified as a substance that improves the disintegration property of the core. This potassium nitrate is an explosive substance known as an explosive component. Furthermore, potassium nitrate is generally known to sinter by heating above 900 ° C.

[0020] Therefore, in the past, the use of a steel mold (core) containing potassium nitrate for the production of steel products having a pouring temperature much higher than that of aluminum production would make potassium nitrate explosive. There was concern about the safety of the work. In addition, if potassium steel is included in the steel mold, the potassium nitrate will sinter at a temperature of 900 ° C or higher to increase the strength of the mold! It was thought to make it worse. For these reasons, as described in the above-mentioned Patent Documents 2 and 3, nitrate nitrate is used for the fabrication of aluminum, but the pouring temperature is much higher than 900 ° C. 1500 ° C It was not considered to be used for forging steel products made as described above.

Patent Document 1: Japanese Patent Laid-Open No. 57-68240

Patent Document 2: Japanese Patent Publication No. 31-7256

Patent Document 3: JP-A-9-57391

Disclosure of the invention

Problems to be solved by the invention

[0021] The present invention has been made to solve the above conventional problems, and its specific purpose is as follows. In the manufacture of steel with a hollow structure, a resin-coated sand for steel that can prevent hot cracks and at the same time effectively reduce the occurrence of hot water wrinkles, a steel mold made using the sand, And to provide a steel product forged by the same mold.

Means for solving the problem

[0022] In order to achieve the above object, the present inventors repeated various experiments. As a result, even when steel structures with extremely high forging temperatures, which were unexpectedly powerful in the past, were produced, there was no concern about explosion even when resin-coated sand for the core was mixed with alkali nitrate and vinsol. I knew that the sex would be significantly improved.

[0023] That is, the resin-coated sand provided by the present invention has, as a basic structure, cocoon sand, 2.5 to 5.0% by weight of phenolic greaves and potassium nitrate based on the cocoon sand. And vinsol is the main feature.

[0024] Further, in the resin-coated sand of the present invention, the phenolic component of the phenolic resin comprises bisphenol A, a residue generated during purification of the bisphenol A, and a derivative of the separated component in the residue. Group power It is preferred to comprise at least one selected.

[0025] Further, the compounding amount of the potassium nitrate is 2 to 50% by weight, and the compounding power of the vinsol is preferably 4.0 to 20% by weight with respect to the phenolic resin.

[0026] Further, the steel mold provided by the present invention is a steel mold having a thickness of 6 to 15 mm and a surface area of 1000 cm ² or more, wherein the resin-coated sand of the present invention is used. The main feature is that it is molded by use. In this case, it is preferable that the hot strength of the saddle type is 120 to 175 NZcm ² ! / ヽ.

[0027] Further, the steel product provided by the present invention is a steel product manufactured using the steel mold of the present invention, the steel product having a thickness of 6 to 15 mm, have a 1000 cm ² or more surface area, and has a main feature in that hot cracks occur铸物surface in contact with the铸型is 70mm or less.

[0028] In addition, the steel product of the present invention has an excellent quality that the steel product's hot water is grade 1 or 2 based on JIS G 0588. Furthermore, the steel product of the present invention preferably has a weight of 35 kg or more. The invention's effect

[0029] The resin-coated sand (RCS) of the present invention contains dredged sand, 2.5 to 5.0% by weight of phenolic rosin, potassium nitrate, and vinsol.

[0030] As described above, the inventors of the present invention have included RCS containing strong potassium nitrate that has not been used in the manufacture of steel products as described above, and a steel product using a mold formed using this RCS. Various experiments were carried out on the fabrication of this. As a result, the following facts have been clarified by adding phenolic resin to RCS at a predetermined ratio different from those in Patent Documents 2 and 3 and potassium nitrate. That is, the injection temperature of molten metal is much higher than that of aluminum, and it has been a concern in the past for the production of steel products with a temperature of 1500-1600 ° C. It became clear that there was no. It was also confirmed that even when nitrate nitrate was included in the steel mold, there was no negative effect on the collapse of the mold due to the sintering of potassium nitrate. On the contrary, by forming a steel mold with potassium nitrate contained in RCS, as explained below, it is very effective in preventing hot cracks and suppressing hot water wrinkles. It was newly revealed that a certain special effect can be obtained.

[0031] This is because potassium nitrate sinters at 900 ° C or higher, but when the temperature of the steel product is much higher than that, the sintered potassium nitrate generates heat due to self-combustion and maintains a high temperature. At the same time, in order to promote the carbonization of phenol resin, even when the molten metal cools and solidifies, even if it shrinks by almost twice the shrinkage amount of aluminum-iron, the bowl itself contracts well by adapting to its behavior. In addition, it is thought that this is due to the fact that the so-called “smoothness” is improved because it holds the porridges firmly. As a result, even if it is a thin-walled and large hollow container, hot cracks are extremely generated. At the same time, the self-heating of potassium nitrate maintains the temperature around the bowl at a high temperature, so that the hot water flow does not stagnate locally and the generation of hot water wrinkles is greatly reduced.

[0032] In the present invention, vinsol is added in addition to the addition of potassium nitrate.

Vinsol resin is derived from pine trees and is a dark, high-melting thermoplastic. Products from Hercules Powder Company are sold on the market. This vinsol resin does not cure three-dimensionally even when it receives heat, so the cushioning effect Has fruit. In order to further enhance this cushioning property, a small amount of petroleum-based rosin rosin or the like can be used in combination. In the present invention, the added force of vinsol promotes softening of the shell cage shape by receiving heat and further improves the properties of the steel plate. On the other hand, vinsol has a tendency to increase the hot strength as rosin. When pouring molten metal, it is necessary to keep the hot strength low enough to maintain the shape of the bowl until the melt is solidified. Here, the hot strength of vinsol is efficiently suppressed by adding potassium nitrate as described above. In other words, the potassium nitrate and vinsol additive is an indispensable requirement for synergistically exhibiting both the above-described properties and the vertical shape retention during solidification of the molten metal.

[0033] That is, in the case of the RCS of the present invention as described above, when a saddle shape (core) is formed by a shell mold method and forged using the same saddle shape (core), potassium nitrate and By the action of binzol, the mold can be deformed at an appropriate timing when the molten metal solidifies and contracts. When the molten steel is poured, it becomes possible to accelerate the thermal decomposition of phenolic resin and reduce the strength of the bowl. As a result, when the molten metal solidifies and shrinks, the shrinkage is not constrained by the saddle shape, so that it is possible to prevent hot cracks from occurring in the steel.

[0034] Furthermore, as described above, since the RCS contains potassium nitrate, the mold itself can generate heat during fabrication. As a result, when the molten metal is poured into a bowl shape, it is possible to prevent the molten metal from being lowered and to make the heat distribution of the molten metal uniform. For this reason, it is possible to obtain a steel frame having a good skin by suppressing the generation of hot water. The blending amount of potassium nitrate at this time is preferably 2 to 50% by weight based on phenol resin. If it is 2% by weight or less, the amount of self-heating is too low and the hot water during pouring will not be smooth, causing hot water wrinkles, and if it is 50% by weight or more, the amount of self-heating is too large. Fat pyrolysis progresses, making it extremely easy to disintegrate, making it impossible to produce a uniform forgery.

[0035] In the present invention, the phenolic component of the phenolic sebum is selected from, for example, bisphenol A, a residue generated during purification of the bisphenol A, and a derivative of a separation component in the residue. Contains at least one species. By including such a phenolic rosin, it is possible to improve the shape of the bowl and to impart more properties. This makes it possible to deform the mold more appropriately as the molten metal solidifies and shrinks during fabrication. The occurrence of intercracking can be very effectively prevented.

[0036] Further, the RCS of the present invention further contains vinsol. As a result, the property can be further improved from the saddle shape, so that the occurrence of hot cracks can be more effectively prevented. In this case, the blending amount of vinsol is preferably 4.0% by weight or more and 20% by weight or less with respect to the phenolic resin. 4. If the amount is less than 0% by weight, the desired improvement in the properties cannot be expected. If the amount exceeds 20% by weight, the hot strength is too low and the bowl shape tends to collapse, and the finished bowl has the desired shape. Is difficult to obtain.

[0037] The steel mold provided by the present invention is a mold used for forging steel products having a thickness of 6 to 15 mm and a surface area of 1000 cm ² or more, and using the RCS of the present invention. Are molded. By performing forging using such a steel mold, it is possible to prevent the occurrence of hot cracks and hot water wrinkles as described above, and to produce a steel product having a good skin. it can

[0038] Further,铸型of the present invention, hot strength is 120~175NZcm ^2. For this reason, it is possible to stably manufacture a steel plate having a desired shape by appropriately maintaining the shape of the steel plate when pouring molten steel.

[0039] The steel product of the present invention is a steel product having a surface area of 6 to 15 mm and a surface area of 1000 cm ² or more, which is manufactured by using the steel mold. In addition, it is an excellent quality product with a hot crack generated on the surface of the surface in contact with the vertical shape of 70 mm or less.

In particular, the steel product of the present invention is a high-quality product that is suppressed so as to be grade 1 or 2 in the class classification based on SJIS G 0588.

[0040] Further, the steel frame is manufactured to have a weight of 35 kg or more. Such steel products have a surface area force of S4000 cm ² or more when the average strength is about 10 mm. Such a thin-walled steel frame having a weight of 35 kg or more and a relatively large size has a large amount of shrinkage at the time of forging, so it has been easy to generate hot cracks in the past. However, the present invention is very useful for such a thin-walled steel frame, and can effectively suppress the occurrence of hot cracks and hot water wrinkles.

Brief Description of Drawings

FIG. 1 is a front view schematically showing a measurement method using a hot deflection measuring device. [2] A schematic cross-sectional view schematically showing a saddle-shaped configuration.

[3] (a) is a front view schematically showing a forged large steel product, and (b) is a cross-sectional view with a plane perpendicular to the thickness direction of the same large steel product. (C) is a II cross-sectional view shown in (a).

圆 4] (a) is a cross-sectional view schematically showing a cross-section of a forged medium-sized steel product, (b) is a cross-sectional view taken along II-II shown in (a), and (c) is It is III-III sectional drawing shown to (a).

[5] (a) is a cross-sectional view schematically showing a cross-section of a forged small steel product, (b) is a side view of the small steel product, and (c) is a side view of the small steel product. It is a bottom view of steel products.

圆 6] A copy of a photograph observing the state of the occurrence of water wrinkles generated in the large steel products of Example 4 and Comparative Example 2.

7] A graph comparing the lengths of the hot water wrinkles generated in the large steel products of Example 4 and Comparative Example 2.

Explanation of symbols

[0042] 1 main mold

2 core

3 Upper mold

4 Lower mold

5 Gate

10 Hot deflection measuring device

11 Large steel products (brackets)

12 Medium size steel products (frame)

13 Small steel product (Small bracket)

H heater BEST MODE FOR CARRYING OUT THE INVENTION

[0043] Hereinafter, preferred embodiments of the present invention will be described in detail.

The RCS in a preferred embodiment of the present invention is 2.0 to 50% by weight of dredged sand, 2.5 to 5.0% by weight phenolic resin and 2.0 to 50% of the same phenolic resin. 4.0% by weight to 20% by weight of potassium nitrate and 20% by weight of the same phenolic resin. And so on.

[0044] As the sand, it is possible to use fire-resistant sand that has been conventionally used for dredging. This dredged sand may be natural sand or artificial sand, and is not particularly limited. Specific examples include, for example, dredged sand, olivine sand, zircon sand, chromite sand, alumina sand, Hue mouth chrome slag, Hue mouth-Neckel slag, converter slag, mullite artificial particles (for example, ITOCHU Ceratech Corporation) Trade names available from the company “Nyiga Sera Beads”), and these reclaimed sand. These may be used alone or in combination of two or more. Among these dredged sands, it is preferable to use dredged sand, and it is more preferable to use dredged sand and recycled sand in combination. Furthermore, by mixing zircon sand, seizure during fabrication can be prevented.

Here, the reclaimed sand is obtained by crushing a lump-shaped lump collected after spreading the reed-shaped sand with a known crusher such as a crusher and subjecting the obtained sand granules to a predetermined regenerating process. is there. In general, examples of the regeneration treatment include a wear-type regeneration treatment that removes deposits adhering to the surface of the sand, and a roasting regeneration treatment that removes the deposit by heat treatment. However, the present invention is not limited to these, and any conventionally known treatment can be adopted as long as it can remove the adhering material of the sand.

[0046] The phenolic greaves function as a binder that binds and holds the particles of the fine sand. The phenolic resin is not particularly limited as long as it is a resin mainly composed of a reaction product of phenols and aldehydes and having a property of being heat-cured in the presence or absence of a curing agent. Absent.

[0047] The phenolic resin is 2.5 to 5.0% by weight, more preferably 2.7% with respect to the sand.

Add to ~ 3.5% by weight. When the content of the phenolic sebum in the sand is less than 2.5% by weight, sufficient strength cannot be imparted to the mold and it becomes easy to cause molding defects. In addition, when steel frames are forged, there is a problem that cracks are generated in the mold during pouring, and a defect called vaning is immediately generated in the mold.

[0048] On the other hand, if the content of phenolic sebum in the sand is over 5.0% by weight, Kneading with sand becomes difficult. In addition, during production, the amount of gas generated increases due to the gasification of phenolic resin. As a result, there is a problem that many gas defects are generated in the manufactured steel frame.

[0049] Specific examples of the phenolic resin include novolac-type phenolic resin, resol-type phenolic resin, nitrogen-containing resol-type phenolic resin, pendyl ether-type phenolic resin, low-expansion phenolic resin, and Modifications produced by mixing or reacting these phenolic resins with, for example, epoxy resins, urea resins, melamine resins, xylene resins, polyamide resins, epoxy compounds, melamine compounds, urea compounds, etc. For example, phenolic resin.

[0050] These phenolic resin may be used alone or in combination of two or more. In addition, when a non-self-curing resin such as a novolak-type phenol resin is used alone, for example, hexamethylenetetramine (hereinafter sometimes abbreviated as hexamine) at the time of mold formation. It is necessary to impart thermosetting properties in combination with an appropriate curing agent. In this case, it is preferable to add hexamine at about 5 to 12% by weight with respect to the phenolic resin. Although there is no restriction | limiting in particular about the usage form of phenol type | system | group resin, Generally, it is a solid of a suitable shape, and is used as a resin liquid or a solution as needed. Also, it can be done by using both solid and liquid.

[0051] The phenol-based榭脂is 30 to 90 weight ^_0/0, preferably comprises low expansion phenol榭脂of 50 to 80 wt%. This low-expansion phenol resin should contain at least one selected from the group power consisting of bisphenol A, a residue produced during purification of the bisphenol A, and derivatives of separated components in the residue. For example, such a phenol rosin as disclosed in Patent Document 1 can be used.

[0052] phenol-based榭脂is, by Dale include such low expansion phenol榭脂30 to 90 weight ^_0/0, no sex better become铸型when molding the铸型Can be used. In this case, if the content of the low-expansion phenolic resin exceeds 90% by weight, there is a risk that a molding failure may occur due to a decrease in the curing rate of the phenolic resin when molding the mold. On the other hand, when the content of low-expansion phenolic resin is less than 30% by weight, baling tends to occur in the steel when forging. [0053] Further, the above-described phenolic resin is used in combination with amino-based, epoxy-based, and bull-based silane coupling agents and Z or lubricants, which are useful for improving the quality of the mold-type strength and lubricity. You can also. Representative examples of the silane coupling agent include y-aminopropyltriethoxysilane, N-β- (aminoethyl) -γ-aminopropyltrimethoxysilane, γ-glycidoxypropyl trimethoxysilane, j8 — (3,4-epoxycyclohexenole) -etyltrimethoxysilane, vinyltrimethoxysilane, buturis (| 8-methoxy) silane, butortris (—methoxyethoxy) silane, and the like. Representative examples of the lubricant include ethylene bis stearic acid amide, methylene bis stearic acid amide, oxystearic acid amide, and methylol stearic acid amide.

[0054] Potassium nitrate, which is one of the essential components of this embodiment, is 2 to 50% by weight, preferably 3 to 25% by weight, and more preferably 5%, based on the weight of phenolic resin (solid conversion). It mix | blends so that it may become ~ 20weight%. If the content of potassium nitrate with respect to phenolic resin is less than 2% by weight, sufficient hot cracking prevention effect cannot be obtained. On the other hand, if it exceeds 50% by weight, the saddle mold is insufficient in strength and may cause molding failure. Considering the safety against explosions during the production of RCS, the content of potassium nitrate should be 50% by weight or less.

[0055] The amount of vinsol is preferably 10% by weight or more and 20% by weight or less, more preferably 10 to 15% by weight, based on the weight of phenolic resin (in terms of solid content). Merge. Thereby, the property can be further improved from the shape of the saddle. For this reason, generation of hot cracks can be more effectively prevented. As vinsol, for example, a pine resin extract or a rosin-extracted rosin residue, specifically, a trade name “bin sol resin” (acid value 95) manufactured by Herxules can be used. In this case, if the content of vinsol in the phenolic greaves is less than 4.0% by weight, it is not possible to expect a further improvement in the properties as required by vinsol. On the other hand, if it exceeds 20% by weight, the hot strength of the mold becomes too low, or gas defects are likely to occur in the steel during forging.

[0056] Further, in the RCS of the present embodiment, in addition to the above components, various additives such as anti-caking agents such as calcium stearate, mold release agents, deodorants, bengara, iron sand, etc. are necessary. Depending on the condition, it can be appropriately blended in a predetermined amount. [0057] It should be noted that the RCS for pig steel as described above is produced by various methods such as a dry hot coating method, a semi-hot coating method, a cold coating method, and a powder solvent method, which have been conventionally performed in the technical field. Can be produced. Among these, it is desirable to use a dry hot coating method in terms of productivity and quality.

[0058] For example, preheated dredged sand is placed in a kneader such as a whirl mixer to adjust the temperature. Next, a phenolic resin (for example, novolak-type phenol resin), potassium nitrate, vinsol, and other necessary additives are supplied in a predetermined amount into a kneader and melted and kneaded for a predetermined time to form a lump. Further, an aqueous hexamine solution is added with stirring and mixing, and the lumps are broken into sand particles by cooling with air blowing, and then calcium stearate is added and kneaded. Thereby, the RCS for steel according to the present embodiment as described above can be obtained. In addition, when supplying potassium nitrate, it is preferable to use it as an aqueous solution having an appropriate concentration, for example, an aqueous solution having a concentration of about 10 to 50% by weight, from the viewpoint of safety during handling.

[0059] Then, by using the above-described RCS for steel, and performing molding according to the shell mold method, a steel mold having a desired shape can be obtained. The mold of the present invention thus obtained is very useful for the production of steel products having a thickness of 6 to 15 mm and a surface area of 1000 cm ² or more.

[0060] That is, when forging is performed using such a steel mold as a core, the action of the nitrate nitrate is improved, and the characteristics of the mold by the low-expansion phenol resin and vinsol are improved. Thus, it is possible to prevent the occurrence of hot cracks in the steel frame to be forged. Furthermore, the saddle mold of this embodiment can heat the saddle mold itself during fabrication because it contains potassium nitrate. As a result, when molten steel is poured into the vertical mold, it is possible to effectively prevent the occurrence of hot water wrinkles in the molten steel by preventing deterioration of the hot water performance, and to produce a steel frame having a good skin. Can be manufactured. In the present invention, the steel mold is not limited to the core as described above, but can be formed as a main mold. Also, the specific molding conditions of the saddle are not particularly limited, and can be appropriately selected according to the usage conditions of the saddle.

[0061] In such铸鋼for铸型, for example configured to be hot strength force 12 0~175N / cm ² of铸型during铸造. By having such hot strength, the steel mold retains the shape of the steel mold when pouring molten steel, and stably produces steel products having a desired shape. Can be built.

[0062] Further, the cold strength of the saddle type for steel is configured to be 900 to 1400 NZcm ² , preferably 1000 to 1360 N / cm ² . If the cold strength of the saddle is less than 900 N / cm ² , baling tends to occur in the steel during forging. On the other hand, if the cold strength exceeds 140 ON / cm ² , gas defects are likely to occur in the porridge.

[0063] The steel product forged using the steel mold as described above has a thickness of 6 to 15 mm and a surface area of 1000 cm ² or more. In addition, the hot crack generated on the surface of the surface in contact with the vertical shape is 70 mm or less per surface area of 1000 cm ² , resulting in excellent quality. In addition, the occurrence of hot water wrinkles is effectively suppressed in such steelware, and for example, the hot water wrinkle generation state is excellent such that the grade classification based on JIS G 0588 shows the first or second class. Has a smooth skin.

Example

Hereinafter, the present invention will be described more specifically with reference to examples. In the following Examples, each RCS produced was subjected to the following tests to evaluate its characteristics.

RCS was shaped to a size of 30πιπι φ X 50mm, and then fired at 250 ° C for 2 minutes to prepare two test pieces 1 (TP1). One TP1 was allowed to cool to room temperature, and its coercive pressure was measured as the cold strength. The other TP1 was detonated at 1000 ° C for 1 minute, and the coercive pressure immediately after that was measured as the hot strength.

[0066] <Measurement of thermal expansion coefficient>

The coefficient of thermal expansion was measured according to JACT test method M-2. That is, TP 1 of 30 mm φ X 50 mm was produced in the same manner as described above, and the length of TP 1 (TP length before heat exposure) was measured. Next, TP 1 was installed in a high-temperature dredged sand testing machine adjusted to a furnace temperature of 1000 ° C. Then, the TP length (TP length after heat exposure) was measured every predetermined time with the same test machine, and the thermal expansion coefficient at each time was calculated by the following formula based on the measurement result.

Thermal expansion coefficient (%) = (TP length after heat exposure TP length before heat exposure) TP length before heat exposure Z 100 [0067] After shaping RCS to a size of 50 x 120 x 5 mm, it was fired at 250 ° C for 40 seconds to produce TP2. The obtained TP2 was fixed to the hot deflection measuring device 10 in a cantilever state as shown in FIG. Subsequently, a preheated heater H was inserted into the lower surface of TP2 to perform heat exposure, and the amount of displacement by which the free end of TP2 was displaced upward and the heat exposure time corresponding to the amount of displacement were measured.

[0068] <Evaluation of hot crack>

The main mold 1 as shown in Fig. 2 was made by the green mold method using the sand. Test piece core 2 was molded by shell molding using RCS. The main mold 1 can be divided into an upper mold 3 and a lower mold 4 in the vertical direction, and a cylindrical space is formed inside.

[0069] Then, the test piece core 2 was coaxially attached to the internal space of the main mold 1 obtained. After that, molten steel was peeled from the pouring gate 5 and poured into a cylindrical steel frame having a thickness of about 10 mm. At this time, low-alloy steel product SCSiMn2 equivalent material was used as the molten steel, and the molten steel was cast at a casting temperature of 1550 ± 10 ° C. The steel product thus obtained was 35 kg in weight, and the surface area of the thin wall portion was 4260 cm ² .

[0070] After forging, the obtained steel product was observed, and the hot cracks occurring in the steel product having the longest crack length were measured. The detection of hot cracks was performed in accordance with the penetrant testing method specified in JIS Z 2343. Based on the measured crack length, hot cracks were evaluated in the following five stages. For the detected hot cracks, the crack length per 1000 cm ² surface area of the steel frame was calculated.

Evaluation index for hot crack: When the crack length is Omm (no hot crack), give an evaluation of "5". Below, the crack length is 100mm or less as "4", and over 100mm and 200mm or less as " “3”, more than 200 mm and less than 300 mm were evaluated as “2”, and more than 300 mm were evaluated as “1”.

[0071] <Evaluation of Yujiwa>

A steel product was produced in the same manner as in the evaluation of the hot crack, and the obtained steel product was visually observed. A steel bowl with strong power that was almost free of hot water wrinkles was evaluated as “◯”, and a hot water wrinkle observed was evaluated as “X”. [0072] [Example 1]

In a whirl mixer (manufactured by Enshu Iron Works Co., Ltd.), 7 kg of domestic silica sand preheated to 150 ° C, novolac type phenol resin (trade name “SP6905” manufactured by Asahi Organic Materials Co., Ltd.); 210 g, 21 g of potassium nitrate, and 40 g of Herxules (trade name: vinzo resin) were kneaded for 40 seconds. Next, an aqueous solution in which 20 g of hexamethylethylenetetramine was dissolved in 105 g of water. Then, the mixture was kneaded while blowing with a blower until the lump of sand collapsed into granules, and then 7 g of calcium stearate was placed in the whirl mixer. RCS was obtained by kneading for 5 seconds.

[Examples 2 to 7 and Comparative Examples 1 to 3]

For Examples 2 to 7 and Comparative Examples 1 to 3, each RCS was changed in the same manner as in Example 1 except that the composition of RCS and its components were changed to the amounts shown in Tables 1 to 3 below. Produced. In Tables 1 to 3, novolac resin B is a novolak type phenol resin, which is a product name `` SP5000HS '' manufactured by Asahi Organic Materials Co., Ltd., which exhibits low expansibility. Is a product name “BP150” manufactured by Asahi Organic Materials Co., Ltd., which is a novolac type phenolic resin that exhibits low expansibility.

Conventional example 1

[0074] As Conventional Example 1, kneaded sand was produced that was formed into a bowl by a room temperature self-curing method that was not a shell mold method. First, 0.9 kg of domestic cinnabar sand and 2.1 kg of reclaimed sand are introduced into the laboratory supplies Kawakita Mixer, and 9 g of product name “E40” manufactured by Asahi Organic Materials Co., Ltd. is added as an organic ester curing agent. The mixture was kneaded for 30 seconds. Thereafter, 45 g of the prepared alkali resole rosin was added and kneaded for 30 seconds to obtain kneaded sand. Each test piece having a predetermined shape can be produced by shaping the obtained kneaded sand and curing it at room temperature.

Conventional example 2

[0075] As Conventional Example 2, kneaded sand that was formed into a bowl by the CO 2 gas method was produced. First, domestic

2

1.5 kg of dredged sand and 1.5 kg of reclaimed sand were placed in a laboratory supplies Kawakita desktop mixer, and 65 g of water glass was added and kneaded for 1 minute. Fill the model with the obtained kneaded sand and use carbon dioxide gas By curing, each test piece having a predetermined shape can be produced. Each cured test piece was left for 24 hours after being removed from the model, and the force was also used for each measurement and evaluation.

[0076] For the samples of Example 17 above, Comparative Example 13 and Conventional Examples 1 and 2, measurement of cold strength, hot strength, and coefficient of thermal expansion was performed. The results of the evaluation of hot water are shown in Table 13 below.

[0077] [Table 1]

s¾

¾007

In Tables 1 and 3 above, as is clear from the comparison between Example 17 and Comparative Example 1 3, hot cracks and hot water wrinkles are generated only by adding RCS to either potassium nitrate or vinsol. It was confirmed that both cannot be suppressed simultaneously. Special In addition, it can be confirmed that by adding vinsol in addition to potassium nitrate in RCS, it is possible to improve the nature and to suppress the occurrence of hot cracks more effectively. Further, as is clear from Examples 1 to 4, RCS containing potassium nitrate, vinsol, and low-expansion phenol resin has a remarkable effect of preventing hot cracking. In particular, by using the RCSs of Examples 4 to 7, it was possible to produce a very high quality steel product free from hot cracks and hot water.

Here, it can be understood from Examples 1 to 7 and Comparative Example 1 that, in particular, in the present invention, the formulation of vinsol greatly contributes to improvement of properties and prevention of hot cracking. According to Comparative Example 1, simply adding potassium nitrate without vinsol is inferior in nature, and the evaluation of hot cracks is as low as 2, and can be understood from Comparative Example 3. In addition, if only vinsol is added without adding nitric acid, the hot cracks and hot water wrinkles cannot be avoided. Here, if the amount of vinsol to phenol rosin is less than 5% by weight, as can be understood from Comparative Examples 1 and 2, the properties are inferior and hot cracks are generated. Many. On the other hand, if the amount of vinsol exceeds 20% by weight, the hot strength will be too low and the mold will be liable to collapse, making it difficult to obtain the desired shape for the finished product.

Next, for each of the RCS of Examples 3 and 4 and Comparative Example 2 and the kneaded sand of Conventional Examples 1 and 2, a core having a predetermined shape is formed, and the core is used to form FIG. A large steel product 11 (bracket) having an actual product shape as shown in Fig. 1 was manufactured. Fig. 3 (b) is a cross-sectional view taken along a plane perpendicular to the thickness direction of the bracket 11 shown in Fig. 3 (a), and Fig. 3 (c) is shown in Fig. 3 (a). It is II sectional drawing shown in FIG. The obtained bracket 11 had an average thickness of about 12 mm, and the surface area of the thin portion was 15200 cm ² .

[0083] When manufacturing the bracket shown in FIG. 3, the main mold was formed by a green mold method. Furthermore, a structural low alloy steel SCSiMn2 equivalent material was injected as a molten steel into a vertical mold, and the molten metal injection temperature was set to 1550 ± 10 ° C.

[0084] For each of the obtained brackets 11, a hot crack was detected in accordance with the penetration flaw detection test method defined in JIS Z 2343, and the length of the detected crack was measured. In addition, the occurrence ratio of cracks per surface area of 1000 cm ^{2 in the} thin wall portion was calculated. In addition, the bracket The raw hot water wrinkles were evaluated based on the appearance test method and grade classification of steel products and skins specified in JIS G 0588.

On the other hand, in Example 2 and Comparative Example 2, the medium-sized steel product 12 (frame) shown in FIG. 4 and the small steel product 13 (small bracket) shown in FIG. 5 were produced. In the production of the medium-sized steel products shown in Fig. 4, carbon steel steel products for welded structures SCW450 equivalent material was used as the molten steel, and the injection temperature of the molten metal was set to 1550 ± 10 ° C. On the other hand, when manufacturing the small steel product shown in Fig. 5, a structural low alloy steel SCSiMn2 equivalent material was used as the molten steel, and the pouring temperature of the molten metal was set to 1550 ± 10 ° C. The other production conditions for these medium and small steel products were the same as those for the large steel products.

[0086] The obtained medium-sized steel product 12 had an average thickness of about 11 mm, and the surface area of the thin-walled portion was 700,000 cm ² . This medium-sized steel product 12 is a component that is very difficult to repair when a hot crack occurs in the hollow interior. For this medium-sized steel product, as in the case of the large steel product, three items were evaluated: hot crack length, crack generation rate per 1000 cm ^{2 of} thin-walled surface area, and hot water wrinkle generation state. Went.

On the other hand, the small steel product 13 had an average thickness of about 12 mm, and the surface area of the thin portion was 2 160 cm ² . This small steel product was evaluated for two items: the length of hot cracks and the occurrence of hot water wrinkles.

Table 4 below summarizes the results of evaluations conducted on the large, medium, and small steel products.

[0088] [Table 4]

[0089] In the evaluation of the large steel product, no hot crack was observed in the steel product obtained in Comparative Example 1. In Comparative Example 1 and Conventional Example 2, although hot cracks were observed in the steel product, the crack length was relatively short, but it was inferior in nature. In contrast, the large steel products manufactured in Comparative Example 2 and Conventional Example 1 had very long hot cracks.

[0090] In addition, in the case of Comparative Example 2, the state of occurrence of hot water wrinkles in large steel products was JIS grades 3 to 4 as shown in FIG. 6 (b). . In FIG. 6, the white portion on the surface of the large steel product indicates the water bath. In addition, in the conventional examples 1 and 2, the state of occurrence of hot water wrinkles was JIS4 class. These are thought to be due to the fact that the molten metal was rapidly cooled by the core when the pour was poured into a bowl, and the hot water performance decreased. On the other hand, in Examples 2 and 4, for example, as shown in a photograph of the large steel product of Example 4 in FIG. It was.

Here, when comparing the length of the hot water wrinkles generated in the large steel products of Example 4 and Comparative Example 2, as shown in FIG. It can be confirmed that the length has been greatly reduced, and the generation of hot water wrinkles has been effectively suppressed. From the above results, it has been clarified that according to the present invention, the effect of preventing hot cracking and the effect of suppressing hot water wrinkles can be obtained remarkably.

[0092] Further, from the evaluation results of the medium-sized and small-sized steel products, it was confirmed that in Example 2, hot cracks did not occur and generation of hot water wrinkles was effectively suppressed. . On the other hand, in Comparative Example 2, the occurrence of hot cracks in the steel product was confirmed. For reference, the positions where hot cracks occurred in the steel product in Comparative Example 2 are shown in FIGS. 4 and 5, respectively. From this result, it has been clarified that a special effect can be obtained by the present invention.

Industrial applicability

[0093] The present invention is effectively applied to the case where a steel mold is formed by using a shell mold method using RCS and a steel frame is forged using the same mold, particularly when a thin steel frame is forged. be able to.

Claims

The scope of the claims

[1] For dredged steel, characterized by comprising dredged sand, 2.5 to 5.0% by weight of phenolic resin, nitric acid lithium and vinsol relative to the dredged sand Resin coated sand.

[2] The phenolic component of the phenolic rosin comprises at least one selected from the group consisting of bisphenol A, a residue generated during purification of the bisphenol A, and a derivative of a separated component in the residue. The resin-coated sand for pig steel according to claim 1, characterized by the above-mentioned.

[3] The resin-coated sun for pig steel according to claim 1 or 2, wherein a blending amount of the potassium nitrate is 2 to 50% by weight with respect to the phenolic resin. De ,.

[4] The resin-coated sand for pig steel according to claim 3, characterized in that it is 4 wt% or more and 20 wt% or less with respect to the phenolic resin.

[5] A steel mold having a thickness of 6 to 15 mm and a surface area of 1000 cm ² or more, and molding using the resin-coated sand according to any one of claims 1 to 4 A steel mold for steel.

[6] The hot strength of the saddle type is 120 to 175 NZcm ² .

A steel mold according to item 5.

[7] A steel product forged by using the steel mold according to claim 5 or 6 and having a thickness of 6 to 15 mm and not less than 1000 cm ² A steel structure having a surface area and having a hot crack generated on the surface of the structure in contact with the mold shape of 70 mm or less.

[8] The steel product according to claim 7, wherein the steel product has a grade classification based on JIS G 0588 of 1 to 2 grades.

[9] The steel product according to claim 7 or 8, wherein the steel product has a weight of 35 kg or more.